Desiccants which desiccate the aboveground part of the plants have been used to make harvest work of crops, such as potato, sunflower, soybean, rape, sorghum and the like, easy. Especially in a case of machine harvest, there is an advantage in an easy operation of a harvest machine and the like. By desiccating aboveground parts of the plants, an outbreak of plant diseases can be controlled. The crops such as sunflower, the crops must be desiccated before pressing oil from the crops after the harvest. In this case, by spraying the desiccant, which desiccate the crop plants before the harvest, to the plants, and lowering the water content of the seeds; the drying cost before pressing oil can be decreased. Also, in a case of soybean, rape and the like, by spraying the desiccant to the plants and accelerating the ripeness of crops; the high-quality harvesting which are uniformly ripen can be gained.
Namely, there are some advantages of desiccating these plants before the harvest. Diquat has been used as a desiccant, however there has been a great demand for higher-performance desiccant.